clientv3/integration: match grpc.ErrClientConnClosing in TestKVNewAfterClose
clientv3/integration: match grpc.ErrClientConnClosing in TestKVNewAfterClose

Signed-off-by: Gyu-Ho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

cockroachdb/etcd,vimalk78/etcd,bluebreezecf/etcd,whuwxl/etcd,lorneli/etcd,lorneli/etcd,gyuho/etcd,mkumatag/etcd,etcd-io/etcd,sebrandon1/etcd,mqliang/etcd,joshix/etcd,li-ang/etcd,etcd-io/etcd,heyitsanthony/etcd,xiang90/etcd,mkumatag/etcd,coreos/etcd,heyitsanthony/etcd,dannysauer/etcd,rnaveiras/etcd,ajityagaty/etcd,bdarnell/etcd,mkumatag/etcd,xiang90/etcd,cockroachdb/etcd,mqliang/etcd,li-ang/etcd,joshix/etcd,sinsharat/etcd,whuwxl/etcd,ajityagaty/etcd,bluebreezecf/etcd,vimalk78/etcd,dannysauer/etcd,sebrandon1/etcd,glevand/coreos--etcd,coreos/etcd,fanminshi/etcd,etcd-io/etcd,rnaveiras/etcd,glevand/coreos--etcd,sinsharat/etcd,rnaveiras/etcd,fanminshi/etcd,ajityagaty/etcd,gyuho/etcd,mqliang/etcd,bdarnell/etcd